import javax.swing.*;
import java.awt.EventQueue;

class Ablak : JFrame() {
    init {
        defaultCloseOperation = JFrame.EXIT_ON_CLOSE
        setSize(300, 200)
    }
}

private fun showGui() {
    val ablak = Ablak()
    ablak.setVisible(true)
}

fun main() {
    EventQueue.invokeLater(::showGui)
}